Flow control methods for controlling flows of data in mobile communication systems have been known. For example, there is a known method in which a maximum allowable transmission rate in a fixed-line zone is determined based on a transmittable rate in the fixed-line zone and a maximum transmittable rate in a radio zone, the transmittable rate being calculated from a band usage rate in the fixed-line zone (see, e.g., Japanese Laid-Open Patent Publication No. 2007-259031). Also, there is a communication control system that determines flow control parameters for packet transfer in a downlink direction based on traffic volume information for each application, radio communication quality information for each terminal, and communication quality information for each application. The radio communication quality information for each terminal includes information about power down or failure in the terminal, deterioration in radio wave conditions, and uplink radio power. The radio communication quality information is carried on a radio data frame transmitted in an uplink direction from the terminal to a wireless base transceiver station (see, e.g., Japanese Laid-Open Patent Publication No. 2000-295276). Additionally, there is a packet transfer rate control method in which a service class is provided for a guaranteed rate for each user, and a weight assigned to a buffer for each service class is updated at predetermined intervals (see, e.g., Japanese Laid-Open Patent Publication No. 2002-57707).
In the related art described above, an error rate of data received from the radio zone is not taken into account in performing flow control. Therefore, it is difficult to balance the amount of transferable data in the radio zone with the amount of data flow in the fixed-line zone.